Repro:
1) On a Chromebook with an attached monitor, open Display settings
2) Try to determine if a display is primary
3) Try to make a secondary display primary

Right now the secondary monitors will get a "Screen" dropdown with the options "Extended display" and "Primary display". Switching to "Primary display" will hide the row and show it on the other monitors.

We should follow the old model: If multiple displays exist, we should show a row for each saying whether it's a "Primary display" or "Extended display". For extended displays, we should include a button to "Make primary".

@bettes what do you think?